Aluminum electrolytic capacitors are widely used in cars, household electric appliances, and so forth. Recently, electrolytic solutions that are little in property degradation of an electrolytic solution and high in sparking voltage have increasingly been desired for aluminum electrolytic capacitors with increase in working voltage of power supplies for vehicle-mounted electrical components and digital home appliances.
As an electrolytic solution for aluminum electrolytic capacitors, disclosed in Patent Document 1 is an electrolytic solution comprising an organic solvent and an electrolyte composed of a quaternary ammonium cation of a compound having a substituted amidine group, such as 1-methylimidazole and 1,2-dimethylimidazoline, and an alkyl phosphate anion. Although the electrolytic solution is little in characteristic degradation and high in sparking voltage, there has been a problem that a short circuit occurs suddenly and therefore it is difficult to use practically.